The polymer microparticles means microparticles composed of a polymer, and the microparticles generally have a wide range of diameters from several tens of nm to several hundreds of μm. Differently from polymer molded products such as films, fibers, injection molded products, and extrusion molded products, polymer microparticles are used for modification and improvement of various materials by utilizing the large specific surface area and the structure of microparticles. Their major uses include modifiers for cosmetics, additives for toners, rheology modifiers for paints and the like, agents for medical diagnosis and examination, and additives for molded products such as automobile materials and construction materials. In particular, they have been in wider use in recent years owing to the advantageous microparticle structure of polymer microparticles, as materials for rapid prototyping and rapid manufacturing, i.e., techniques to produce custom-made molded products combining with laser processing technologies.
Furthermore, recently, as such polymer microparticles, in fields of electronic information materials and the like such as liquid crystal displays, there are increasing demands for polymer microparticles that are high in heat resistance and solvent resistance, and more uniform in particle diameter distribution.
We previously found a process for producing polymer microparticles wherein two kinds of polymers are dissolved into a solvent, and by bringing a poor solvent into contact with the emulsion comprising respective phases, polymer microparticles are precipitated (WO 2009/142231).
This process has features that adjustment of emulsion diameter is easy and the particle diameter distribution is narrow, and it is an effective manner capable of making microparticles for wide range of kinds of polymers and an effective manner for obtaining microparticles composed of a highly heat-resistant polymer.
Although the conventional processes disclose that different kinds of polymers are dissolved into a solvent, and after an emulsion is formed, microparticles are formed by bringing a poor solvent into contact therewith, in case where a highly heat-resistant polymer, particularly, a crystalline polymer, is made into microparticles, there is a problem that the viscosity of the system becomes high at the step for forming the emulsion, and the particle diameter distribution tends to become wider.
There is therefore a need to provide a process of stably producing high-quality polymer microparticles having a smaller particle diameter distribution in the production process of polymer microparticles wherein two kinds of polymers are dissolved into a solvent and polymer microparticles are precipitated by bringing a poor solvent into contact with an emulsion comprising respective phases, and polymer microparticles produced by the process.